As Supreme Court Justice Potter Stewart famously said, when confronted with a decision about what constituted pornography, the definition is hard, but “I know what it is when I see it.” An all-encompassing definition of fatigue is similarly difficult, but everyone knows what fatigue feels like. The profound lassitude that signals an oncoming flu is a gluey, mesmerizing state of mind and body that renders one incapable of remembering ever feeling good, of imagining ever feeling energetic again, or of conceiving of a desire to participate in any physical, social or mental activity beyond crawling beneath the bedcovers.  

The perception of energy failure

 Where there is life, there is fatigue. All plants and animals run on energy produced in little chemical factories (mitochondria) in every cell. The ultimate source of biologic energy is the sun’s nuclear energy, converted to usable form by plants and transferred to animals as food. The more complex the living thing, the more obvious the need for periods of rest and recovery to replenish energy. When the demand energy use outpaces the time needed for recovery, or when normal function is derailed by illness, drugs or toxins, fatigue is the name we give to what we feel, mentally and physically. To the research scientist, fatigue is a by-product of numerous little proteins (cytokines) produced by the immune system to protect us from outside invaders and internal disorders like cancer. How these proteins create the feeling of fatigue is a mystery, but there is admirable logic in a system that commandeers a patient’s energy, drive and ambition and sends him packing off to bed while an internal battle rages.  

Voluntary fatigue

Less admirable is our ability to override the biology that produces tiredness, and to become passive, cranky and sleep-deprived. In fact, most complaints of fatigue reflect the deliberate choice to ignore the symptom and would and yield to simple lifestyle changes – if one were willing and able to sleep more, lose weight, eat regular, well-balanced meals, exercise enough, manage time wisely, avoid smoking, excess alcohol, and junk food, and engage in satisfying work. In our culture these are tall orders, and a background level of fatigue is often accepted as normal. 

Evaluation of fatigue 

New, unexpected and persistent tiredness, however, may signal underlying illness or environmental stress and warrants a serious evaluation, with clear communication about exactly what fatigue means to the patient. First, a description of the patient’s normal “background energy” is important. Some people are full of energy from the day they are born. Others are inveterate couch potatoes, happy to sit and watch life go by. The feeling of fatigue that prompts one to see a doctor is, by definition, different from the patient’s normal state, but the doctor sees only a snapshot in time. Patients and families should never be shy about volunteering information about what life used to be like. 

Defining the symptom

Next, the language used by patients to describe fatigue needs to be clear. “I’m tired” sometimes means “I’m weak,” and “I’m weak” sometimes means “I’m tired,” but in the jargon of medicine, weakness means loss of muscle strength. Provided that they exert full effort, tired people can generate normal muscle power upon request, but people with strokes or nerve and muscle diseases cannot. Separating weakness from fatigue is the doctor’s first job – otherwise he may head off on the wrong diagnostic road. Description of the activities affected by tiredness and/or weakness, and characterization of changes fatigue brings to daily life are crucial to the process of diagnosis.   

Finding the source

Once a doctor understands the way fatigue affects life for a patient, he moves on to a “review of systems” – a top to bottom list of questions ranging over all the body’s organs, looking for clues to the presence of heart, kidney or liver disease, diabetes, cancer, sleep apnea, restless leg syndrome, insomnia, degenerative neurologic diseases like Parkinson’s, autoimmune illnesses like lupus or MS, chronic infections, eating disorders and problems of the thyroid, adrenal and pituitary glands. A good doctor will then delve into the lifestyle and life events surrounding the appearance of fatigue. Tiredness is a complex, high level symptom that may also originate in the mind – it is one of the cardinal symptoms of depression. 

Is it the drugs

Next comes a careful inventory of all medicines in use, prescription and non-prescription. New fatigue symptoms may parallel the addition of new drugs (even antibiotics can cause fatigue). An inventory of potential toxins and hazards in the environment may turn up a faulty furnace producing carbon monoxide or exposure to toxins such as volatile hydrocarbons that can damage the part of the brain called the cerebellum – a major player in energy balance. 

Following the clues

 Following a good, inquisitive medical history, a complete physical exam (the kind that requires undressing) may turn up other clues that suggest the need for more than “routine” tests. Fatigue is messenger bringing information about conditions ranging from minor to mortal. When not readily explained, fatigue warrants the best of our medical tools to ferret out the source of trouble. The first step though, is still a careful history and physical examination. Without these, advanced medical technological evaluation of fatigue is little better than a fishing expedition sent to sea with no information about where the fish hang out. 

                                                    The Chronic Fatigue Syndrome

Definition:

Profound, life-altering fatigue lasting more than 6 months.

May follow a viral infection, but no test abnormalities persist along with the fatigue.

Physical and mental activities both worsen symptoms.

Variety of accompanying symptoms: weakness, muscle and skeletal aches and pains, impaired memory, lack of drive, poor sleep.

Diagnosis:

No specific tests, other than exclusion of other illnesses that produce these symptoms, among others. CFS is a “diagnosis of exclusion.”

Conditions to be excluded:

Chronic infections, mononucleosis, autoimmune disorders (lupus, M.S.), hypothyroidism, low adrenal function, sleep apnea, cancer (particularly pancreatic), obesity, eating disorders, drug and alcohol abuse, major psychiatric disturbances: schizophrenia, depression.